Appendix G. Configuring
TwinView

The TwinView feature is only supported on NVIDIA GPUs that
support dual-display functionality, such as the GeForce2 MX,
GeForce2 Go, Quadro2 MXR, Quadro2 Go, and any of the GeForce4,
Quadro4, GeForce FX, or Quadro FX GPUs. Please consult with your
video card vendor to confirm that TwinView is supported on your
card.

TwinView is a mode of operation where two display devices
(digital flat panels, CRTs, and TVs) can display the contents of a
single X screen in any arbitrary configuration. This method of
multiple monitor use has several distinct advantages over other
techniques (such as Xinerama):

A single X screen is used. The NVIDIA driver conceals all
information about multiple display devices from the X server; as
far as X is concerned, there is only one screen.

Both display devices share one frame buffer. Thus, all the the
functionality present on a single display (e.g. accelerated OpenGL)
is available with TwinView.

You may also use any of the following options, though they are
not required:

Option "TwinViewOrientation" "<relationship of head 1 to head 0>"
Option "ConnectedMonitor" "<list of connected display devices>"

Please see detailed descriptions of each option below.

Detailed Description of Options

TwinView

This option is required to enable TwinView; without it, all
other TwinView related options are ignored.

SecondMonitorHorizSync,SecondMonitorVertRefresh,

You specify the constraints of the second monitor through these
options. The values given should follow the same convention as the
"HorizSync" and "VertRefresh" entries in the Monitor section. As
the XF86Config man page explains it: the ranges may be a comma
separated list of distinct values and/or ranges of values, where a
range is given by two distinct values separated by a dash. The
HorizSync is given in kHz, and the VertRefresh is given in Hz.

These options are normally not needed: by default, the NVIDIA X
driver retrieves the valid frequency ranges from the display
device's EDID (see Appendix D, X
Config Options for a description of the "UseEdidFreqs"
option). The SecondMonitor options will override any frequency
ranges retrieved from the EDID.

HorizSync,VertRefresh,

Which display device is "first" and which is "second" is often
unclear. For this reason, you may use these options instead of the
SecondMonitor versions. With these options, you can specify a
semicolon-separated list of frequency ranges, each optionally
prepended with a display device name. For example:

These options are normally not needed: by default, the NVIDIA X
driver retrieves the valid frequency ranges from the display
device's EDID (see Appendix D, X
Config Options for a description of the "UseEdidFreqs"
option). The "HorizSync" and "VertRefresh" options override any
frequency ranges retrieved from the EDID or any frequency ranges
specified with the "SecondMonitorHorizSync" and
"SecondMonitorVertRefresh" options.

MetaModes

A single MetaMode describes what mode should be used on each
display device at a given time. Multiple MetaModes list the
combinations of modes and the sequence in which they should be
used. When the NVIDIA driver tells X what modes are available, it
is really the minimal bounding box of the MetaMode that is
communicated to X, while the "per display device" mode is kept
internal to the NVIDIA driver. In MetaMode syntax, modes within a
MetaMode are comma separated, and multiple MetaModes are separated
by semicolons. For example:

"<mode name 0>, <mode name 1>; <mode name 2>, <mode name 3>"

Where <mode name 0> is the name of the mode to be used on
display device 0 concurrently with <mode name 1> used on
display device 1. A mode switch will then cause <mode name 2>
to be used on display device 0 and <mode name 3> to be used
on display device 1. Here is a real MetaMode entry from the X
config sample config file:

Option "MetaModes" "1280x1024,1280x1024; 1024x768,1024x768"

If you want a display device to not be active for a certain
MetaMode, you can use the mode name "NULL", or simply omit the mode
name entirely:

"1600x1200, NULL; NULL, 1024x768"

or

"1600x1200; , 1024x768"

Optionally, mode names can be followed by offset information to
control the positioning of the display devices within the virtual
screen space; e.g.:

"1600x1200 +0+0, 1024x768 +1600+0; ..."

Offset descriptions follow the conventions used in the X
"-geometry" command line option; i.e. both positive and negative
offsets are valid, though negative offsets are only allowed when a
virtual screen size is explicitly given in the X config file.

When no offsets are given for a MetaMode, the offsets will be
computed following the value of the TwinViewOrientation option (see
below). Note that if offsets are given for any one of the modes in
a single MetaMode, then offsets will be expected for all modes
within that single MetaMode; in such a case offsets will be assumed
to be +0+0 when not given.

When not explicitly given, the virtual screen size will be
computed as the the bounding box of all MetaMode bounding boxes.
MetaModes with a bounding box larger than an explicitly given
virtual screen size will be discarded.

A MetaMode string can be further modified with a "Panning
Domain" specification; e.g.:

"1024x768 @1600x1200, 800x600 @1600x1200"

A panning domain is the area in which a display device's
viewport will be panned to follow the mouse. Panning actually
happens on two levels with TwinView: first, an individual display
device's viewport will be panned within its panning domain, as long
as the viewport is contained by the bounding box of the MetaMode.
Once the mouse leaves the bounding box of the MetaMode, the entire
MetaMode (i.e. all display devices) will be panned to follow the
mouse within the virtual screen. Note that individual display
devices' panning domains default to being clamped to the position
of the display devices' viewports, thus the default behavior is
just that viewports remain "locked" together and only perform the
second type of panning.

The most beneficial use of panning domains is probably to
eliminate dead areas -- regions of the virtual screen that are
inaccessible due to display devices with different resolutions. For
example:

"1600x1200, 1024x768"

produces an inaccessible region below the 1024x768 display.
Specifying a panning domain for the second display device:

"1600x1200, 1024x768 @1024x1200"

provides access to that dead area by allowing you to pan the
1024x768 viewport up and down in the 1024x1200 panning domain.

Offsets can be used in conjunction with panning domains to
position the panning domains in the virtual screen space (note that
the offset describes the panning domain, and only affects the
viewport in that the viewport must be contained within the panning
domain). For example, the following describes two modes, each with
a panning domain width of 1900 pixels, and the second display is
positioned below the first:

"1600x1200 @1900x1200 +0+0, 1024x768 @1900x768 +0+1200"

Because it is often unclear which mode within a MetaMode will be
used on each display device, mode descriptions within a MetaMode
can be prepended with a display device name. For example:

"CRT-0: 1600x1200, DFP-0: 1024x768"

If no MetaMode string is specified, then the X driver uses the
modes listed in the relevant "Display" subsection, attempting to
place matching modes on each display device.

TwinViewOrientation

This option controls the positioning of the second display
device relative to the first within the virtual X screen, when
offsets are not explicitly given in the MetaModes. The possible
values are:

"RightOf" (the default)
"LeftOf"
"Above"
"Below"
"Clone"

When "Clone" is specified, both display devices will be assigned
an offset of 0,0.

Because it is often unclear which display device is "first" and
which is "second", TwinViewOrientation can be confusing. You can
further clarify the TwinViewOrientation with display device names
to indicate which display device is positioned relative to which
display device. For example:

"CRT-0 LeftOf DFP-0"

ConnectedMonitor

With this option you can override what the NVIDIA kernel module
detects is connected to your video card. This may be useful, for
example, if any of your display devices do not support detection
using Display Data Channel (DDC) protocols. Valid values are a
comma-separated list of display device names; for example:

"CRT-0, CRT-1"
"CRT"
"CRT-1, DFP-0"

WARNING: this option overrides what display devices are detected
by the NVIDIA kernel module, and is very seldom needed. You really
only need this if a display device is not detected, either because
it does not provide DDC information, or because it is on the other
side of a KVM (Keyboard-Video-Mouse) switch. In most other cases,
it is best not to specify this option.

Just as in all X config entries, spaces are ignored and all
entries are case insensitive.

G.1.
Frequently Asked TwinView Questions

Nothing gets displayed on my second monitor; what is
wrong?

Monitors that do not support monitor detection using Display
Data Channel (DDC) protocols (this includes most older monitors)
are not detectable by your NVIDIA card. You need to explicitly tell
the NVIDIA X driver what you have connected using the
"ConnectedMonitor" option; e.g.:

Option "ConnectedMonitor" "CRT, CRT"

Will window managers be able to appropriately place windows
(e.g. avoiding placing windows across both display devices, or in
inaccessible regions of the virtual desktop)?

Yes. The NVIDIA X driver provides a Xinerama extension that X
clients (such as window managers) can use to discover the current
TwinView configuration. Note that the Xinerama protocol provides no
way to notify clients when a configuration change occurs, so if you
modeswitch to a different MetaMode, your window manager will still
think you have the previous configuration. Using the Xinerama
extension, in conjunction with the XF86VidMode extension to get
modeswitch events, window managers should be able to determine the
TwinView configuration at any given time.

Unfortunately, the data provided by XineramaQueryScreens()
appears to confuse some window managers; to work around such broken
window mangers, you can disable communication of the TwinView
screen layout with the "NoTwinViewXineramaInfo" X config Option
(please see Appendix D, X
Config Options for details).

Be aware that the NVIDIA driver cannot provide the Xinerama
extension if the X server's own Xinerama extension is being used.
Explicitly specifying Xinerama in the X config file or on the X
server commandline will prohibit NVIDIA's Xinerama extension from
installing, so make sure that the X server's log file does not
contain:

(++) Xinerama: enabled

if you want the NVIDIA driver to be able to provide the Xinerama
extension while in TwinView.

Another solution is to use panning domains to eliminate
inaccessible regions of the virtual screen (see the MetaMode
description above).

Why can I not get a resolution of 1600x1200 on the second
display device when using a GeForce2 MX?

Because the second display device on the GeForce2 MX was
designed to be a digital flat panel, the Pixel Clock for the second
display device is only 150 MHz. This effectively limits the
resolution on the second display device to somewhere around
1280x1024 (for a description of how Pixel Clock frequencies limit
the programmable modes, see the XFree86 Video Timings HOWTO). This
constraint is not present on GeForce4 or GeForce FX chips -- the
maximum pixel clock is the same on both heads.

Do video overlays work across both display devices?

Hardware video overlays only work on the first display device.
The current solution is that blitted video is used instead on
TwinView.

How are virtual screen dimensions determined in
TwinView?

After all requested modes have been validated, and the offsets
for each MetaMode's viewports have been computed, the NVIDIA driver
computes the bounding box of the panning domains for each MetaMode.
The maximum bounding box width and height is then found.

Note that one side effect of this is that the virtual width and
virtual height may come from different MetaModes. Given the
following MetaMode string:

"1600x1200,NULL; 1024x768+0+0, 1024x768+0+768"

the resulting virtual screen size will be 1600 x 1536.

Can I play full screen games across both display
devices?

Yes. While the details of configuration will vary from game to
game, the basic idea is that a MetaMode presents X with a mode
whose resolution is the bounding box of the viewports for that
MetaMode. For example, the following:

produce two modes: one whose resolution is 2048x768, and another
whose resolution is 1600x600. Games such as Quake 3 Arena use the
VidMode extension to discover the resolutions of the modes
currently available. To configure Quake 3 Arena to use the above
MetaMode string, add the following to your q3config.cfg file:

Note that, given the above configuration, there is no mode with
a resolution of 800x600 (remember that the MetaMode "800x600,
800x600" has a resolution of 1600x600"), so if you change Quake 3
Arena to use a resolution of 800x600, it will display in the lower
left corner of your screen, with the rest of the screen grayed out.
To have single head modes available as well, an appropriate
MetaMode string might be something like:

"800x600,800x600; 1024x768,NULL; 800x600,NULL; 640x480,NULL"

More precise configuration information for specific games is
beyond the scope of this document, but the above examples coupled
with numerous online sources should be enough to point you in the
right direction.